Ocular redness - I: Etiology, pathogenesis, and assessment of conjunctival hyperemia

Abstract

The translucent appearance of the conjunctiva allows for immediate visualization of changes in the circulation of the conjunctival microvasculature consisting of extensive branching of superficial and deep arterial systems and corresponding drainage pathways, and the translucent appearance of the conjunctiva allows for immediate visualization of changes in the circulation. Conjunctival hyperemia is caused by a pathological vasodilatory response of the microvasculature in response to inflammation due to a myriad of infectious and non-infectious etiologies. It is one of the most common contributors of ocular complaints that prompts visits to medical centers. Our understanding of these neurogenic and immune-mediated pathways has progressed over time and has played a critical role in developing targeted novel therapies. Due to a multitude of underlying etiologies, patients must be accurately diagnosed for efficacious management of conjunctival hyperemia. The diagnostic techniques used for the grading of conjunctival hyperemia have also evolved from descriptive and subjective grading scales to more reliable computer-based objective grading scales.

Keywords: Conjunctiva; Conjunctival vasculature; Conjunctivitis, ocular redness, conjunctival hyperemia; Microcirculation.

Figure 1:

The arterial supply (red) and venous draining (blue) of the conjunctival tissue.

Figure 2:

The immunopathological mechanisms triggered on allergen exposure in the conjunctiva.

Figure 3:

The signaling pathway activated by histamine through H1 and H2 receptors activated in the vascular smooth muscle cells, leading to vasodilation of microvessels in the conjunctiva.

Figure 4:

Neurogenic vasodilation trigger by calcitonin gene related peptide (CGRP) in the vascular smooth muscle cells, causing vasodilation of conjunctival microvessels.

Figure 5:

The region of interest (ROI) marked by the observer before analysis of the Ocular Redness Index by the software using a preset formula. (From Amparo et al., 2013)